The North Fork Holston River (NFHR), located in southwestern Virginia and northeastern Tennessee, is part of the Upper Tennessee River Basin. The NFHR originates in Bland County, Virginia and flows southwest approximately 112 river miles until its confluence with the South Fork Holston River (SFHR) in Tennessee to create the Holston River. A former chlorine plant (site) operated from 1950 to 1972 and contributed mercury to the river. The plant ceased operations in 1972. Mercury concentrations in surface water decreased significantly after the removal of sediment from a section of the NFHR in 1982 and again when outfall treatment commenced in 1994.

Fish Index of Biotic Integrity (IBI) collections were made in 1988, and the status of fish

fauna were considered repeated in an effort representative habitat

to be “poor” to document types within

to “fair” (YMA 1989). In 2005, fish IBI collections were

changes over a particular

time.

Fish collections were

sampling

reach

to

obtain

a

conducted in representative

assemblage of fish species from each sampled area. Bulk sediment samples were total mercury and methylmercury analysis in conjunction with the fish collections.

collected

for

Total mercury in sediment was not detected at the upstream reference location (RM 85.4). Downstream total mercury concentrations ranged from a minimum of 0.0964 mg/kg at

RM 48.9 to

a maximum

mercury at

downstream

of 4.97 mg/kg at RM 81.4 (near locations were greater than the

the site). upstream

Detected

results for

total

reference

location.

The

methylmercury concentration at the upstream reference location was 0.000034 Downstream methylmercury concentrations in the NFHR ranged from a minimum of

sampling locations (RM 39 and RM 17.5), which had methylmercury the concentrations detected at the upstream reference location.

concentrations

less

than

Fish IBI scores calculated using the Ridge and Valley scoring system (TVA 2005) ranged from 46 to 54, representing classifications from “Fair/Good” to “Good/Excellent”. The 2005 IBI data was compared to historical IBI data presented from the 1988 YMA IBI study (YMA 1989). The 1988 IBI utilized the Blue Ridge scoring criteria instead of the recently developed Ridge and Valley scoring criteria, which is approximately 2 to 4 points lower than the Blue Ridge scoring system, and therefore, more stringent. Despite the use of a more stringent scoring system in the current study, there has been improvement in the fish communities in the NFHR at all downstream sampling locations except RM 61.5, which maintained a “Fair” classification for both time periods. Conversely, the IBI classification for the reference sampling location rated as “Good” in 1988 but declined to “Fair” in the 2005 study.